the direct application of parathion-methyl and omethoate induced
slight mutagenesis only at some concentrations and was very toxic
at higher concentrations, preventing both revertants and background
growth in concentrations equal to or higher than
500 lg (co-incubation flask)1
. According to De Flora et al.
(1992), toxicity to bacteria is indicated by the disappearance of
the background lawn. The sudden increase in bacterial toxicity
was probably due to cell death. This behavior is in agreement with
the results reported by Cortés-Eslava et al. (2001), who observed
parathion-methyl toxicity beginning at concentrations of
45 lg (co-incubation flask)1 in the plant cell–microbe assay using
the S. typhimurium strain TA98. Dime